common/boneblack-sdcard-preparation: add missing space

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

common/boneblack-sdcard-preparation.tex

@@ -21,7 +21,7 @@ \section{Prepare the SD card}
 your system: look at the output of \code{cat /proc/partitions} and
 find your SD card. In general, if you use the internal SD card reader
 of a laptop, it will be \code{mmcblk0}, while if you use an external
-USB SD card reader, it will be \code{sdX} (i.e\code{sdb}, \code{sdc},
+USB SD card reader, it will be \code{sdX} (i.e \code{sdb}, \code{sdc},
 etc.). {\bf Be careful: \code{/dev/sda} is generally the hard drive of
   your machine!}